1. Field of Invention
This disclosure is directed to a scrambling method and apparatus for use with any composite or component video transmission system.
2. Overview of Video Scrambling Systems
The various video scrambling systems implemented or proposed to date have in one way or another attempted to prevent a viewer from viewing certain pre-recorded or transmitted video programs. Many of these systems are complicated and require rather expensive implementation in the scrambler or descrambler or both.
Such a system is described in John O. Ryan U.S. Pat. No. 4,916,736, issued Apr. 10, 1990, and assigned to Macrovision Corporation, directed to having time sequential information signals having a time reference and an active video portion encrypted (scrambled) by time shifting the active video portion towards and away from the line reference signal in pseudo-random fashion before recording on tape or disk or transmission to the user. The signals are descrambled by an inverse time shifting technique.
Another system is described in John O. Ryan U.S. Pat. No. 5,058,157, issued Oct. 15, 1991, and assigned to Macrovision Corporation, directed to a similar time shifting of the active video in the scrambling process. The descrambling process is a much less expensive implementation whereby the descrambled signal contains some time base errors that are within the capture or correction range of the follow-on monitor/receiver.
There are many other scrambling systems and methods that use such techniques as video inversion, line shuffling, and line cutting and rotation. These techniques suffer from expense problems or their inability to be recorded.